1. Field of the Invention
This invention relates to thermally responsive valve devices, and more particularly to a thermally responsive valve device having dual operating valve function which closes and and opens two passages, respectively.
2. Description of the Prior Art
Various thermally responsive valve devices of this type have been used in emission control systems of automobiles. For example, a valve device of the wax operating type has been previously proposed. However, wax operating valves are commonly subject to a loss of wax when subjected to overpressures, and such loss of wax tends to change the operating temperatures of the valve. Wax operating valves have a complicated structure and a relatively high production cost. On the other hand, a valve device of the bimetal operating type has also been proposed. However, since the bimetal operating valve device needs two valve members positioned in the two passages and respective valve seats, the valve device is complicated in structure and high in cost.